This invention relates to novel rotary drill bits suitable for cutting semi-hard, hard and abrasive rocks and to a novel boring or drilling process employing the novel rotary drill bits.
Drill holes in mines, quarries and analogous mining or prospecting ground generally have a diameter of 30 to 200 mm. Two types of drill bits are presently used for boring these holes, the choice between them is dictated by the nature of the rocks through which the hole must be drilled. For non-abrasive rocks having a hardness value of less than 800 bars, such as limestone or marl, rotary drill bits can be used. However, for harder or more abrasive rocks, such as sandstone or granite, rotary drill bits are not efficient enough and percussive hammers or rotopercussion drill bits are used. The latter are more powerful but are more complex and thus more costly. Moreover, the noise level associated with their use is higher, therefore more disturbing.
In both types of drilling bits, rock is cut by cutter edges reinforced by plates of tungsten carbide. In both cases, dust which develops during drilling is discharged by a fluid injected into the bore hole through the drill tubing. The fluid is usually water under pressures ranging between 0 and 40 bars, or air under a pressure of about 5 bars. In order to achieve more efficacious boring, the use of water jets having very high pressures on the order of up to 4000 bars has been considered. However, this method is not commercially feasible since the energy costs are excessive. Furthermore, the use of these high pressure jets does not lead to uniform results since softer grounds are preferentially attacked.
It is therefore an object of the present invention to provide a novel drilling bit which can be used efficiently to drill both non-abrasive softer rock, and harder or abrasive rock. It is another object to provide a novel cutting edge for such drill bits. It is a further object to provide a novel drilling process which employs such a novel drilling bit. Other objects of the invention will be apparent to those skilled in the art to which the present invention pertains.
To achieve these objects, the invention includes a rotary drive bit characterized by a cutting edge which is protected by a fluid film or fluid jets under a pressure of 1000 to 4000 bars which are directed or passed from the drill bit parallel to the drilling axis and perpendicular to the cutting edges.
In another article of manufacture aspect, the invention relates to a novel cutting edge for rotary drill bits which comprises means for injecting from the drill head a small quantity of fluid under very high pressure parallel to the boring axis of the rotary drill bit and perpendicular to the cutting edges.
The invention relates to novel boring tubing which comprises means for introducing fluid under very high pressure, and means for introducing fluid under low pressure, both of which are adapted for use in combination with the novel drill bit cutter edge of the invention.
In a further article of manufacture aspect, the invention relates to a novel rotary drill bit outfitted with two fluid injection means and adapted for use with the novel cutting edge and the novel boring tubing of the invention.
In a process aspect, the invention relates to a novel drilling method which employs one or more of the novel boring tubing, cutting edge and rotary drill bit of the invention.
The cutting edge according to this invention is comprises at least one inserted plate which includes at least one miniature hole, adapted to release a fluid, preferably water under a very high pressure, e.g., 1000 to 4000 bars, at a fluid flow rate of 5 to 25 liters/min. The water under high pressure is passed from the drill bit, from a position forward from the cutting edge in the direction of rotation, parallel to the axis of drilling to form a protective film over the cutting edge. The cutting edge also comprises one laterally positioned larger hole (ranging between 1 to 8 mm, for example) for passing a low pressure fluid, e.g., air or water. When air is used, the pressure is generally in the range of about 5 bars, and in the case of water, the pressure is generally about 0 to 40 bars. This supplementary injection is primarily intended to carry away, through the borehole, the rock particles produced from the boring resulting from the combined action of the cutting edge and the high pressure fluid, because the flow rate of the high pressure fluid, viz., 5 to 25 liters/min, is insufficient to ensure a quick enough removal of the cutting dust which is necessary to enable rapid drilling of the borehole.
The bit body is attached to boring tubing made up of two concentric tubes providing respective fluid injection circuits connected to the corresponding smaller and larger holes of the cutting edge.
The rotary drilling machine which is operatively connected to the boring tubing supporting the cutting edge also comprises a double fluid injection circuit.